The present invention, in some embodiments thereof, relates to electron paramagnetic resonance and, more particularly, but not exclusively, to a electron paramagnetic resonance system useful for oxygen monitoring.
Any imbalance in tissue oxygen levels may affect metabolic homeostasis and lead to pathophysiological conditions. For instance, the role of hypoxia in cancer treatment and wound healing has been well documented. There are only two technologies in mainstream clinical use that directly measure oxygenation status: arterial catheters and transcutaneous oxygen monitoring (TCOM) using electrodes. These technologies are primarily used for critical-care monitoring.
Arterial catheters are most commonly placed and maintained within the radial artery and measure oxygen levels in the blood that indicate systemic oxygen availability but not actual tissue oxygenation. This is a very important distinction because adequate oxygenation of the blood is not always accompanied by tissue uptake of oxygen. The invasive nature of monitoring oxygenation levels with a catheter in a blood vessel is also accompanied by significant risks to the patient, e.g., direct access of bacteria from the external environment to the patient's blood stream along the surface of the catheter, occlusion of the artery by the catheter resulting in critical ischemia to the hand, etc.
Electrode-based TCOM is the only non-invasive, clinically-approved methodology that estimates tissue oxygenation by measuring the diffusion of extracellular oxygen through the skin. The method is quantitative and is the only method that measures oxygen delivery to an end organ (in this case, the skin). It has been used to monitor oxygen levels in the skin, especially for premature infants, but also for adults in the intensive care setting. It is used to determine the healing capacity of wounds, but is only used in about 2% of chronic wound cases. For this procedure, the patient's skin must be shaved and the top layer removed. Electrodes are then clamped to the patient's skin via fixation rings and heated to 100 degrees Fahrenheit. In some cases this process can cause first-degree burns on the patient, especially infants. After heating, the user performs oxygen measurement of the underlying tissue. The entire process can last from 45 to 90 minutes. These drawbacks, along with a high rate of user error (some experts estimate error to be as high as 60% due to procedural complexity), leads to a low usage rate of this technology.
Measuring oxygen concentration (pO2) by electron paramagnetic resonance (EPR) involves the use of an exogenous probe including paramagnetic material in either solid or soluble form. The changes in the relaxation times (T2) of the EPR probe are caused by the interaction of two paramagnetic species molecular oxygen and the EPR probe. These reversible oxygen-induced changes in the relaxation times are used to quantify pO2. EPR oximetry offers unique advantages over other existing oximetry methods, including high sensitivity to pO2 and high functional specificity. Unlike BOLD MRI and pulse oximetry, which measure blood oxygen saturation, EPR oximetry measures the tissue oxygen concentration directly. In the last fifteen years, several sensitive, nontoxic, particulate oximetry probes have been developed. The long-term stability of some of these probes in tissue has also been established. More importantly, particulate-based EPR oximetry is “minimally invasive” because the particulate probe is implanted only one time, and the subsequent measurements are carried out without any invasive procedure.
However, existing hardware system limitations make the use of EPR oximetry for clinical purposes less ideal. As most conventional EPR systems are large, bulky units with restrictive spacing between the magnet poles, refinements in EPR system hardware would make this technology more appealing from a clinical standpoint. The movement towards smaller, portable EPR systems would be of substantial benefit to both the end user (e.g., clinicians, clinical technicians, etc.) and the patients for whom such a system would be intended. As a smaller, portable system, the EPR oximetry system would have the capability to be transported from room to room, rather than have the patient brought to a separate location. In critical-care settings, this would be most useful, as moving the patient is often not an option.